Plasma display panels (hereinafter, referred to as “PDP”s) are flat display apparatuses that make use of radiation caused by gas discharges. PDPs can easily perform high-speed display and be large in size, and are widely used in fields such as video display apparatuses and public information display apparatuses. There are two types of PDPs, namely the direct current type (DC type) and alternating current type (AC type). In particular, surface discharge AC type PDPs have been commercialized due to having a great amount of technological potential in terms of lifetime and increases in size.
FIG. 12 is a schematic view showing a structure of discharge cells, or discharge units, of a general AC type PDP. The PDP 1x shown in FIG. 12 is constituted by a front panel 2 and a back panel 9 that are sealed together. The front panel 2 as a first substrate includes a front panel glass 3. A plurality of display electrode pairs 6, each composed of a scan electrode 5 and a sustain electrode 4, are disposed on one surface of the front panel glass 3. A dielectric layer 7 and a surface layer 8 are layered sequentially to cover the display electrode pairs 6. The scan electrode 5 and the sustain electrode 4 are respectively composed of transparent electrodes 51 and 41 and bus lines 52 and 42 layered thereon.
The dielectric layer 7 is made of low-melting glass with a softening point of approximately 550° C. to 600° C. and has a current limiting function that is peculiar to the AC type PDP.
The surface layer 8 protects the dielectric layer 7 and the display electrode pairs 6 from ion bombardment resulting from plasma discharge, efficiently emits secondary electrons in a discharge space 15 and lowers firing voltage of the PDP. Generally, the surface layer 8 is made, by the vacuum deposition method or the printing method, using magnesium oxide (MgO) that has high secondary electron emission characteristics, high sputtering resistance, and high optical transmittance. Note that, instead of the surface layer 8, a protective layer (also, referred to as a protective film) having the same structure as the surface layer 8 and exclusively for ensuring the secondary electron emission characteristics may be disposed.
On the other hand, the back panel 9 as a second substrate includes a back panel glass 10 and a plurality of data (address) electrodes 11, which are used for writing image data, disposed on the back panel glass 10 so as to intersect the display electrode pairs 6 at a right angle. On the back panel glass 10, a dielectric layer 12 made of low-melting glass is disposed to cover the data electrodes 11. Disposed on the dielectric layer 12, at the borders with the neighboring discharge cells (not illustrated), are barrier ribs 13 of a given height, made of low-melting glass. The barrier ribs 13 are composed of pattern parts 1231 and 1232 that are combined to form a grid pattern to partition a discharge space 15. Phosphor ink of either R, G, or B color is applied to the surface of the dielectric layer 12 and the lateral surfaces of the barrier ribs 13, and baked to form phosphor layers 14 (phosphor layers 14R, 14G, and 14B).
The front panel 2 and the back panel 9 are sealed together at opposing edge portions of both panels such that a longitudinal direction of the display electrode pairs 6 is orthogonal to a longitudinal direction of the data electrodes 11 with the discharge space 15 therebetween. The sealed discharge space 15 is filled with a rare gas such as Xe—Ne or Xe—He as a discharge gas, at a pressure of some tens of kPa. This concludes a description of the structure of the PDP 1x. 
A gradation expression method (e.g. an intra-field time division gradation display method) that divides one field of an image into a plurality of subfields (S.F.) is used to display images in the PDP.
In recent years, electrical appliances are desired to be driven with low power, and the same desire exists for PDPs as well. In PDPs that display high definition images, discharge cells are made smaller in size and increased in number. Therefore, in order to surely produce write discharges, operating voltage is required to be increased in the small discharge spaces. The operating voltage of PDPs depends on a secondary electron emission coefficient (γ) of the surface layer. Here, γ is a value that depends on materials of the surface layer and discharge gases, and γ is known to increase as work functions of the materials decrease. Increased operating voltage becomes an obstacle to drive PDPs with low power. In view of this, Patent Literature 1 discloses a surface layer including (i) SrO as the main component and (ii) CeO2, and technology for stably discharging SrO at low voltage.
[Citation List]
[Patent Literature]
[Patent Literature 1]
Japanese Patent Application Publication No. S52-116067